Silicon surface chemistry is of fundamental technical significance because of the ubiquitous role of silicon in modern technology; yet silicon/organic chemistry is only just beginning to be investigated. Virtually all microprocessor chips in electronic products are based upon crystalline silicon wafers. Control of silicon surface chemistry is crucial to allow access to technologically functional thin films for fabrication of new electronic devices. In 1990, Canham and co-workers showed that silicon wafers could be etched using hydrofluoric acid to produce a porous layer that is only a few microns thick (termed porous silicon) and exhibits photoluminescence upon exposure to UV light (Canham, L. T. Appl. Phys. Lett. 1990, 57, 1046). The surface of porous silicon (Si) is populated with metastable Si—Hx bonds (x=1,2,3), exposed Si—Si bonds, and defects such as open valence, “dangling” Si atoms. Potential applications for porous silicon include uses as chemical sensors, biosensors, optoelectronic devices such as electroluminescent displays, photodetectors, mass spectrometry (desorption ionization on silicon or DIOS), interfacing with neurons and other nerve cells, and as a matrix for photopumped tunable lasers. As a result, modification and characterization of photoluminescent porous silicon surfaces has become an area of intense interest.
Recent developments in the functionalization of porous silicon have enabled Si—C bonds to be formed on the porous-Si surface by attacking the weak Si—Si bonds of exposed nanocrystalline submaterial with Grignard or alkyllithium reagents. Grignard and alkyllithium transmetallation and the use of Lewis acid catalysis have also been used to exploit the great population of surface Si—H bonds. Thermal, radical-mediated, and UV photolytic alkene hydrosilylation has also been reported for flat Si and Si hydride surfaces. In general, chemistry that works on porous silicon also applies to flat Si (100) and Si (111) surfaces based on substantial literature precedent. Additionally, using the Si surface as a semiconducting electrode, several workers have recently reported electrochemical Si—C bond formation by direct grafting, an approach with few parallels to soluble, molecular silane chemistry.
The present invention is directed to a new method of functionalizing the Si surfaces by electrochemically grafting terminal alkynes to silicon resulting in two distinct surface derivations depending on the polarity of the surface bias. Cathodic electrografting (CEG) directly attaches alkynes to the surface, whereas anodic electrografting (AEG) of alkynes yields an alkyl surface.